The following relates generally to wireless communication, and more specifically to device-to-device (D2D) synchronization. Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communications system may include a number of base stations, each simultaneously supporting communication for multiple mobile devices. Base stations may communicate with mobile devices on downstream and upstream links. Each base station has a coverage range, which may be referred to as the coverage area of the cell. The base stations provide the devices within the coverage area with various services, like synchronization. The range of network synchronization can be further extended, if the (in-coverage) devices also transmit synchronization signals, based on the network timing, on some resources allocated for device-to-device communications. At times, clusters of collocated devices may become isolated from the rest of the network. When a mobile device, or group of mobile devices, moves outside the (extended) coverage area of all base stations associated with a communications network, the mobile devices may lose coverage, with a resultant loss of services provided by the communications network. The group of mobile devices may maintain some level of synchronization with one another, but as time progresses while they are isolated, the synchronization with the network may become unreliable. The group of mobile devices may use all of the available resources in a dense mobile device scenario. As a result, these mobile devices will not be able to receive any further synchronization signals on these occupied resources and may remain isolated, even if they move within range of a synchronization signal with reliable network timing.